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Many automated lighting luminaires contain a mechanical iris, which reduces the aperture size of the main output. Martin fixtures, such as the MAC Viper Profile or MAC Quantum Profile, include this handy sizing tool.
While the iris is commonly used to make the output narrower, there are many other modifications you can achieve with an iris. Lighting designers (LD) and programmers often use the following tricks to maximize the abilities of their automated lights’ irises.
#1 Change Gobo Imagery
One of the most fun tricks with an iris is to change the look of gobos. This works great whether the gobo is used for projection or as an aerial effect. By reducing the aperture, you reveal less of the original gobo artwork. Oftentimes, this results in a completely different look than the full gobo.
Essentially, you are cropping off a portion of the original art in a symmetrical fashion. As you vary the iris size, you are also adjusting the crop. For the best results, try to find gobos that drastically alter their look when you delete certain portions.
#2 Combine with Prism
Do you know what happens when you iris down the open aperture and insert a 3-facet prism? The result is an amazing set of three dots (or beams) that can rotate around each other.
This same trick works with any type of prism. For instance, a round 8-facet prism looks very busy with the full aperture, but drop the iris down, and now you have created a “Gatling gun” effect.
Imagine taking this further and combining it with the first trick by adding a gobo. Some very stunning looks are possible with an iris, a prism and a gobo!
#3 Create Fireworks
The action of seeing a beam open and close its iris can look stunning in the air or on a projected surface. As the size of the beam changes, the output goes from a large column of light to a tight beam. However, by combining with a shutter and a gobo, the iris can instantly help create realistic firework effects or other exciting animations.
Using lighting console effects or building a chase, you can instruct lights to open the shutter, iris out and then immediately close the shutter. If you do this with multiple fixtures in a random order, then you can create a fireworks-looking effect on a projected surface. Alternately, you can run this in reverse to create droplets or other creative looks.
#4 Reduce Output
While it is true that an iris is typically used to reduce the size of the primary output, it can also be used to reduce the total light output. Since the iris is blocking some of the light, there is always a light loss when using an iris. This can be used to your advantage, though, when using a profile fixture as a wash (with frost) or when using a wash fixture, such as the MAC Viper Wash DX.
Since the reduction of intensity is uniform from around the aperture, it is often a different type of dimming than using the dimmer blades. Many LD’s find dimming a wash via the iris much smoother and cleaner. To achieve a total blackout, they first reduce the iris and then follow with the dimmer.
#5 Make Fun Shapes
If your fixture has both an iris and framing shutters, such as the MAC Viper Performance, you can combine these two features to create unique shapes. With only one system or the other, you cannot create curved images or half moons. Once again, adding in gobos or even a prism can energetically change the look even further!
Mechanical irises within automated luminaires are extremely valuable tools. Remember, they are much more than a simple beam size reducer. Most hard-edged fixtures either use a mechanical iris or have aperture-reducing steps on a gobo wheel (such as the MAC Axiom Hybrid). In either case, the above tricks can add creativity and excitement to any production.